Identification of sub-band-gap absorption features at the HfO2∕Si(100) interface via spectroscopic ellipsometry

Abstract

Spectroscopic ellipsometry is used to characterize charge trapping defect states in thin $\mathrm{Hf}{\mathrm{O}}_2$ gate dielectric films deposited by atomic layer deposition on chemically oxidized $p$ -type Si (100) substrates. The intensity of specific absorption features detected below the band gap of $\mathrm{Hf}{\mathrm{O}}_2$ at 2.9 and $4.75\mathrm{eV}$ is clearly distinguished from the Si critical points; however, repeating this spectroscopic evaluation for identical $\mathrm{Hf}{\mathrm{O}}_2$ films deposited and annealed on fused silica substrates results in no defect features detected. The $\mathrm{Hf}{\mathrm{O}}_2∕\mathrm{Si}\left(100\right)$ results, therefore, suggest these oxygen deficient defects are not intrinsic to $\mathrm{Hf}{\mathrm{O}}_2$ but reside primarily at the interface with the silicon substrate. The feasibility of utilizing spectroscopic ellipsometry to identify stoichiometric variations at the $\mathrm{Si}{\mathrm{O}}_2∕\mathrm{Si}\left(100\right)$ interface and the corresponding changes associated with the electrical performance is presented.